Method and system for producing a digital terrain model

Abstract

A method and system for calculating a digital terrain model (DIM) for a target portion of the surface of the Earth. A digital elevation model (DEM) for the target portion specifies an elevation for target points on the Earth within the portion. A digital surface model (DSM) specifies the elevation above the target point of an obstructing surface. Elevation errors in the DEM are corrected. A curvature correction is done using the DSM. A model is calibrated using reference points using statistical techniques or machine learning. A model using reference points for predicting the amount of local elevation correction needed at each target point as a function of terrain curvature is employed. The models are applied at each target point of the DEM to produce the DTM.

1 . A method performed by a computer processor for calculating a digital terrain model (DTM) for a target portion of the surface of the Earth, the method comprising:
 receiving a digital elevation model (DEM) for the target portion, the DEM specifying an approximate elevation for each of a plurality of target points on the Earth within the portion;   receiving a digital surface model (DSM), produced using a spaceborne or airborne vehicle that has imaged the target portion, specifying, for each of the target points, the elevation above the target point of an obstructing surface visible from the spaceborne or airborne vehicle when the vehicle is in flight above the target point or, where there is no obstructing surface above the target point, the elevation of the target point;   correcting elevation errors in the DEM caused by land cover, including vegetation obstructing the view of the target points, and by terrain curvature, wherein the land cover correction is done using imagery and related ancillary data, the imagery and ancillary data being acquired at a period of time roughly corresponding to the time of the acquisition of DEM data, the imagery being radiometrically corrected for the effects of topography on image brightness, wherein the curvature correction is done using the DSM;   calibrating a model using reference points, each reference point having accurate values of latitude, longitude and elevation, using statistical techniques or machine learning, for predicting the amount of local elevation correction needed at each target point as a function of land cover;   calibrating a model using reference points, each reference point having accurate values of latitude, longitude and elevation, using statistical techniques or machine learning, for predicting the amount of local elevation correction needed at each target point as a function of terrain curvature;   applying the models at each target point of the DEM to produce the DTM.   
     
     
         2 . The method of  claim 1 , wherein the land cover correction is done by extracting at each target point the land cover characteristics from the imagery and ancillary data, predicting the amount of local elevation correction as a function of land cover using the land cover model, and correcting the elevation of the target point elevation accordingly. 
     
     
         3 . The method of  claim 1 , wherein the curvature correction is done by calculating at each target point the local terrain curvature of the DSM, predicting the amount of local elevation correction as a function of terrain curvature using the terrain curvature model, and correcting the elevation of the target point elevation accordingly. 
     
     
         4 . The method of  claim 1 , wherein calculation of the land cover model is done by receiving imagery and ancillary data collected by a spaceborne or airborne vehicle of the target portion, correcting the imagery for the radiometric effects of topography and sun position in the case of optical imagery, or topography and the view angle in the case of radar images, extracting the corrected image values at the latitude and longitude of the reference points, calculating the difference between the elevation of reference points and the corresponding elevation of the DEM at the latitudes and longitudes or the reference points, and establishing a relationship between the image values and the corresponding elevation differences by calibrating a statistical or machine learning model. 
     
     
         5 . The method of  claim 1 , wherein calculation of the terrain curvature model is done by calculating the local terrain curvature at every point of the DSM, extracting the terrain curvature values at the latitude and longitude of the reference points, calculating the difference between the elevation of reference points and the corresponding elevation of the DEM at the latitudes and longitudes or the reference points, and establishing a relationship between the terrain curvature values and the corresponding elevation differences by calibrating a statistical or machine learning model. 
     
     
         6 . The method of  claim 1 , wherein the imagery and ancillary data are acquired at a period of time within 7 years of the acquisition of DEM data. 
     
     
         7 . The method of  claim 1 , wherein the reference points are geodetic survey points, global navigation satellite system (GNSS) points, airborne light detection and ranging (LIDAR) points, or spaceborne LIDAR points. 
     
     
         8 . The method of  claim 1 , wherein the accurate values of the latitude and longitude of the reference points are accurate to within 10 m and the accurate values of the elevations of the reference points are accurate to within 1 m. 
     
     
         9 . The method of  claim 1 , wherein the DEM is produced using data collected by an interferometric synthetic aperture radar system. 
     
     
         10 . The method of  claim 1 , wherein the DEM is produced using a combination of image matching and photogrammetry. 
     
     
         11 . The method of  claim 1 , wherein the DSM is produced using data collected by an interferometric synthetic aperture radar system. 
     
     
         12 . The method of  claim 1 , wherein the DSM is produced using a combination of image matching and photogrammetry. 
     
     
         13 . The method of  claim 1 , wherein the imagery is optical imagery. 
     
     
         14 . The method of  claim 1 , wherein the imagery is radar imagery. 
     
     
         15 . The method of  claim 1 , wherein the ancillary data includes date, sun position, and view angle corresponding to the imagery. 
     
     
         16 . The method of  claim 1 , wherein the approximate elevation for each of the plurality of target points is accurate to within 30 m. 
     
     
         17 . The method of  claim 1 , further comprising receiving, via an electronic interface, data and imagery of the target portion of the surface of the Earth collected by a spaceborne or airborne vehicle, and (b) computing the DSM for the target portion using the received data and imagery. 
     
     
         18 . The method of  claim 1 , further comprising receiving, via an electronic interface, data and imagery of the target portion of the surface of the Earth collected by a spaceborne or airborne vehicle, and (b) computing the DEM for the target portion using the received data and imagery. 
     
     
         19 . A system comprising one or more processors and a digital memory in electronic communication with the one or more processors, wherein the one or more processors are configured to perform the method of  claim 1 . 
     
     
         20 . A system comprising one or more processors, a digital memory in electronic communication with the one or more processors, a data interface, wherein the one or more processors are further configured to (a) receive, via the interface, data and imagery of a target portion of the surface of the Earth collected by a spaceborne or airborne vehicle, (b) compute a digital surface model (DSM) for the target portion using the received data and imagery, and (c) perform the method of  claim 1 . 
     
     
         21 . The system of  claim 20 , wherein the one or more processors are further configured to (a) receive, via the interface, data and imagery of a target portion of the surface of the Earth collected by a spaceborne or airborne vehicle, and (b) compute a digital elevation model (DEM) for the target portion using the received data and imagery.